1. Field of the Invention
The present invention relates to an image forming apparatus such as a digital Multi Functional Peripheral (MFP) that scans an original document for conversion into image data and records the image data on a sheet of paper, and to an image forming method.
2. Description of the Related Art
In an image forming apparatus, such as, a recent digital MFP including a copying function, a facsimile function, a printing function, and a scanner function, etc. or a copier, when making a copy, image data of a scanned original document is supplied to a printer and recorded on a sheet of paper.
When signing up a maintenance agreement for such an image forming apparatus, an agreement is made, for example, as follows: “A basic charge paid up front provides maintenances/services including supplies of consumables such as toner up to 2400 sheets per month with a printing rate of 20%.” Under such a maintenance agreement, when an actual result of usage is 2000 sheets per month with an average printing rate of 20%, the user could have printed 400 more sheets, which means a loss to the user.
On the other hand, when an actual result of usage is 3000 sheets with an average printing rate of 20%, the user has to pay an additional fee for the extra 600 sheets since the number of prints exceeds a range of the agreement. When an actual result of usage is 2400 sheets with an average printing rate of 30%, if the printing rate (black letter/character rate) is neither calculated nor managed as the result of usage, an additional fee does not occur, which means a loss to the seller. In other words, 2400 sheets with an average printing rate of 30% is equivalent to 3600 sheets with a printing rate of 20%, which means that consumables for the extra 1200 sheets are provided within the range of the basic charge.
As described above, when an actual average printing rate is higher than the supposed printing rate, unless an additional fee is paid, toner that exceeds an amount of toner included in the basic charge is used for the basic charge, which means a loss to the seller. In contrast, when the actual average printing rate is lower than the supposed printing rate, all of the toner included in the basic charge cannot be used up, which means a loss to the user. In order to eliminate such disadvantages, the maintenance agreement should be made based on a contract printing rate and the contract number of printed sheets.
In order to recognize the time required to replace a toner cassette, a conventional method proposes to calculate a black rate at the time of image forming, i.e., calculate the proportion of the number of black pixels to the total number of pixels per page, and to display the number of remaining recordable sheets that will be recorded when the image forming is continued with the present black rate. The number of remaining recordable sheets is calculated based on an average black rate in the case where a standard image is formed, the average number of image-formed sheets, an average black rate of all of the images that have been formed since the cassette replacement up to the present time, and the number of sheets on which the images have been formed up to the present time.
In order to set and collect an appropriate usage fee for each recording function such as a printer function and a copying function or the like, another conventional art suggests to calculate an accumulated usage fee for each function. That is, it is suggested to store a usage fee per sheet of recording paper, which is set for each function, and to calculate and store the accumulated usage fee for each function based on the number of used sheets for each function and the usage fee per sheet.
In order to keep a usage fee of an image forming apparatus within the budget, another conventional art suggests to add a printing rate each time a printing operation is performed, and to notify the user when a value of a printing rate adding counter reaches an upper-limit counter value, which is set in advance, or when the counter value is likely to exceed the upper-limit counter value.
When making a maintenance agreement based on a contract printing rate and the contract number of printed sheets, the number of remaining recordable/printable sheets may be displayed by applying the calculation for the number of remaining recordable/printable sheets to the maintenance agreement. However, when the number of remaining recordable/printable sheets decreases it cannot be determined whether or not such copying operation exceeds the number of remaining recordable/printable sheets unless a copying operation is actually performed. In other words, since a printing rate of an original document to be copied is not known the number of recordable/printable sheets may become negative when the number of original documents is less than the number of remaining recordable/printable sheets and such original documents are copied.
For example, in the case where the number of recordable/printable sheets with a contract printing rate of 20% is 30, when the number of original documents to be copied is 20 with a printing rate of 40%, such number of original documents is equivalent to 40 with the contract printing rate. As a result, the number of recordable/printable sheets will be minus 10.